I noticed that the following measurements are different between the Gen3 G20/G20SF and Gen4 G20 (did not check out the G29 as not interested in that):

Length: 209mm, 204mm, 193mm (Gen3, Gen3SF, Gen4)

Width: In mm, same. In inches, Gen4 is .01 inches wider.

Barrel Height: 32mm, 32mm, 20mm (Gen3, Gen3SF, Gen4). I wonder if 20mm is a typo and should be 30mm, or if that is for real? I know almost nothing about firearm design, but, that seems like a significant unpublished change.

Barrel Length: In mm, same. In inches, Gen4 is .01 inches longer. Given the width change above, I wonder if this is an errata on the Gen4, or, was errata on the Gen3s and they corrected on the Gen4.